Time and the Geological Record 295 



and goats, are as striking as the difference of the dogs. The 

 carnivora again, illustrate the imperfection of artificial 

 classification, the leopards and tigers and their kind, show 

 many creatures but a little apart, which are fertile in union. 

 The differences, which in historic time under man's obser- 

 vation, have been seen to arise or merge or disappear, in the 

 form and organization of animal life (and even more in 

 vegetable), are such, that it is clear that distinct species do 

 so arise, and probably have always so arisen. The lack 

 of continuity, in the existing, and in the geological series, 

 is easily understood. The forms which were transitory, 

 being produced by fast changing circumstances, would most 

 probably disappear, while those which were sustained by 

 environment long lasting, became more numerous and en- 

 during, and so more likely to leave enduring records. These 

 were only a few of the many experimental forms, those 

 selected by nature out of many experiments; and preferred 

 because they fitted their conditions, like seed cast upon cul- 

 tivated ground. Between these favored forms were many 

 whose fugitive efforts were only stepping stones from one 

 type to another; and in their quick disappearance we have 

 lost the evidence of relationship. Such a process still con- 

 tinues, or would continue if circumstances favored it. Sup- 

 pose for example that all the varities of living dogs were 

 exterminated by human custom or demand, except very 

 large and very small; and no dogs were bred except the 

 mastiffs and the toy terriers ; and suppose that the influences 

 which discriminated against the medium sized animals con- 

 tinued to operate against any new tendency toward such 

 size. These two types of dogs, already fairly established, 



